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<div class="titlepage"><div><div><h3 class="title">
<a name="asio.reference.synchronous_socket_operations"></a><a class="link" href="synchronous_socket_operations.html" title="Requirements on synchronous socket operations">Requirements
      on synchronous socket operations</a>
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<p>
        In this section, <span class="emphasis"><em>synchronous socket operations</em></span> are those
        member functions specified as two overloads, with and without an argument
        of type <code class="computeroutput">error_code&amp;</code>:
      </p>
<pre class="programlisting"><span class="bold"><strong><span class="emphasis"><em>R f</em></span></strong></span>(<span class="emphasis"><em><span class="bold"><strong>A1</strong></span></em></span> a1, <span class="emphasis"><em><span class="bold"><strong>A2</strong></span></em></span> a2, ..., <span class="emphasis"><em><span class="bold"><strong>AN</strong></span></em></span> aN);
<span class="bold"><strong><span class="emphasis"><em>R f</em></span></strong></span>(<span class="emphasis"><em><span class="bold"><strong>A1</strong></span></em></span> a1, <span class="emphasis"><em><span class="bold"><strong>A2</strong></span></em></span> a2, ..., <span class="emphasis"><em><span class="bold"><strong>AN</strong></span></em></span> aN, error_code&amp; ec);
</pre>
<p>
        For an object <code class="computeroutput">s</code>, the conditions under which its synchronous
        socket operations may block the calling thread (C++Std [defns.block]) are
        determined as follows.
      </p>
<p>
        If:
      </p>
<p>
        &#8212; <code class="computeroutput">s.non_blocking() == true</code>,
      </p>
<p>
        &#8212; the synchronous socket operation is specified in terms of a <span class="emphasis"><em>POSIX</em></span>
        function other than <code class="computeroutput"><a href="http://www.opengroup.org/onlinepubs/000095399/functions/poll.html" target="_top"><code class="computeroutput"><span class="identifier">poll</span><span class="special">()</span></code></a></code>,
      </p>
<p>
        &#8212; that <span class="emphasis"><em>POSIX</em></span> function lists <code class="computeroutput">EWOULDBLOCK</code> or
        <code class="computeroutput">EAGAIN</code> in its failure conditions, and
      </p>
<p>
        &#8212; the effects of the operation cannot be established immediately
      </p>
<p>
        then the synchronous socket operation shall not block the calling thread.
        [<span class="emphasis"><em>Note:</em></span> And the effects of the operation are not established.
        &#8212;<span class="emphasis"><em>end note</em></span>]
      </p>
<p>
        Otherwise, the synchronous socket operation shall block the calling thread
        until the effects are established.
      </p>
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<td align="right"><div class="copyright-footer">Copyright &#169; 2003-2018 Christopher M. Kohlhoff<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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